Minimizing server downtime

Suppose that you are responsible for a typical LAMP server running Debian. The goal is to have the needed security updates and minimize downtime. Unfortunately, due to installation of security updates, services need to be restarted, and sometimes (after kernel updates) even a reboot is required. Here are some tips that will help you shrink the time of service unavailability.

1. Upgrade your key services (apache, php and mysql) separately from the rest of software. Reason: if you just run "apt-get dist-upgrade" to upgrade everything, then your MySQL server will be stopped at the beginning of the whole upgrade and started only at the end, after unpacking all other packages. So, run "apt-get install mysql-server" before "apt-get dist-upgrade" to minimize the delay.
2. If you know that kexec works on your hardware, use it: apt-get install kexec-tools. This way, you will avoid the long time (sometimes more than a minute) while your server shows useless BIOS screens. Instead of rebooting to the BIOS, the old kernel will load the new kernel directly and pass control to it, thus avoiding the delay.